Replies using Copilot on MacOS Outlook shows HTML code when email is received

Question

Replies using Copilot on MacOS Outlook shows HTML code when email is received

Scott Townsend 5

When using Copilot (New Outlook on MacOS) to write a reply, it looks perfect. When received, some HTML code is showing in the email, often several lines. Appears to be only when received in Classic Outlook on Windows, New and Outlook Web are OK. Multiple recipients report seeing the code. Message is HTML format.

Example:

.copilot-citation-indicator {display: inline-block;width: 13px;height: 13px;border: 1 px solid

#d1d5db;border-radius: 4px;text-align: center;line-height: 11px;font-size: 10px;font-family: -

apple-system, Roboto;font-weight: 500;margin: 0 3px;background-color: #ffffff;color:

#374151;vertical-align: middle;box-shadow: 0 1px 2px rgba(0, 0, 0, 0.05);} .ms-outlook-mobile-

dark-mode .copilot-citation-indicator {background-color: #374151;color: #f9fafb;border: 1px

solid #6b7280;border-radius: 4px;}

This was in the middle of the reply, there was no citation despite the code eluding to a citation, was just a few basic lines of text.

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Answer 1

Dora-T 12,980 Microsoft External Staff Moderator

Hi Scott Townsend

Thank you for reaching out to the Microsoft Q&A Forum and for sharing the details of your issue.

I tested this scenario in my environment (macOS Tahoe 26.3.1(a) with Outlook version 16.108, and Classic Outlook for Windows as the receiving client), and it worked as expected on my side.

To better understand your situation, could you please help confirm the following:

The exact version of Outlook and macOS you are currently using
Whether this issue started recently or has been occurring for some time
Whether it happens with all emails or only specific messages

This information will help narrow down the possible cause and provide more accurate guidance.

Please understand that our initial reply may not always immediately resolve the issue. However, with your help and more detailed information, we can work together to find a solution.

I look forward to your response.

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

Scott Townsend 5 Reputation points

2026-04-15T03:03:30.67+00:00

Hi there, the issue only happens when using Copilot 365 to generate the reply in Outlook. Doesn't appear to do it when using Copilot to draft a new email.

Outlook Mac 16.108

MacOS macOS 15.6.1

Issue appears to have started this month, no reports of recipients seeing the HTML code prior to this, though we may not have been notified. Doesn't occur with every message, maybe 20% of replies generated using Copilot.

Screenshot showing what it looks like for the recipient, blocked out personal info, red square around the HTML code and the message Outlook displays:
[Moderator note: personal info removed]
Dora-T 12,980 Reputation points Microsoft External Staff Moderator

2026-04-15T03:50:50.3766667+00:00

Please note that our forum is a public platform, and we will modify your question to hide your personal information in the description. Kindly ensure that you hide any personal or organizational information the next time you post an error or other details to protect personal data.

Hi Scott Townsend

Thank you for your quick response and for sharing those details. I understand that this behavior occurs only when using Copilot to generate replies, happens intermittently, and started recently.

In my test environment, I’m not seeing the same issue when replying with Copilot. For reference, I’ve included a screenshot below for comparison.

Could you also help confirm the version of Classic Outlook for Windows that the affected recipients are using? It would be helpful to know whether they are all on the same version or if there are differences.

Since this behavior appears to have started recently, you may consider rolling back Outlook for Mac to an earlier version, such as 16.105, to see whether the issue still occurs.

-Open any Office app > Help > Check for Updates, then clear the checkbox for Automatically keep Microsoft Apps up to date

-Quit all Office apps

-Go to Applications, select Microsoft Outlook, and move it to Trash

-Install version 16.105 from this link: Update history for Office for Mac - Office release notes | Microsoft Learn

If the issue persists after that, I recommend raising a support ticket with Microsoft Support for further investigation. Please note that creating a support ticket typically requires Global Administrator permissions. If you’re an end user or do not have this role, please contact your organization’s administrator for assistance.

For further instructions, you can follow this guide: Get support - Microsoft 365 admin | Microsoft Learn.

Please understand that this is a public, peer‑to‑peer community forum. While moderators and community members can share guidance and experiences, we do not have access to advanced diagnostic tools or backend systems for deeper investigation.

Thank you again for your understanding and patience.
Dora-T 12,980 Reputation points Microsoft External Staff Moderator

2026-04-16T02:02:25.5933333+00:00

Hi Scott Townsend

May I know if you have checked on my recent response?

Please let me know if you have any further questions.
Scott Townsend 5 Reputation points

2026-04-16T02:10:18.2033333+00:00

Thanks, we will try 16.105 and see how that goes. Cheers.
Dora-T 12,980 Reputation points Microsoft External Staff Moderator

2026-04-16T02:19:34.6433333+00:00

Hi Scott Townsend

Please let me know if there are any updates on your end.

Best regards,
Dora-T 12,980 Reputation points Microsoft External Staff Moderator

2026-04-17T01:04:15.1333333+00:00

Hi Scott Townsend

Is there any update from you?

If yes, please feel free to let me know.
Scott Townsend 5 Reputation points

2026-04-23T18:43:23.9933333+00:00

Hi, we rolled back to 16.105 and so far no further issues. Many thanks for your help and support!!
Dora-T 12,980 Reputation points Microsoft External Staff Moderator

2026-04-24T07:39:59.84+00:00

Hi Scott Townsend

Thank you for taking the time to get back to me.

I'm glad to hear that the issue has been resolved. If you have any other questions or run into any issues in the future, please feel free to reach out again.

Best regards,

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Replies using Copilot on MacOS Outlook shows HTML code when email is received

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